High Performance Steels: Microstructure Development and Advanced Characterization II
Sponsored by: TMS Structural Materials Division, TMS: Steels Committee
Program Organizers: Jonah Klemm-Toole, Colorado School of Mines; Ana Araujo, Vesuvius USA; C. Tasan, Massachusetts Institute of Technology; Richard Fonda, Naval Research Laboratory; Amit Behera, QuesTek Innovations LLC; Benjamin Adam, Oregon State University; Krista Limmer, Devcom Army Research Laboratory; Kester Clarke, Los Alamos National Laboratory

Tuesday 2:30 PM
March 21, 2023
Room: Aqua F
Location: Hilton

Session Chair: Richard Fonda, Naval Research Laboratory; Benjamin Adam, Oregon State University


2:30 PM  Invited
Advanced Microstructural Characterization of Long-term Thermal Ageing Effects in Ferritic-Martensitic Steels: David Sprouster1; B Adam2; A Koziol2; L Rolly2; C Huotilainen3; J Tucker2; 1Stony Brook University; 2Oregon State University; 3TerraPower LLC
    We describe our current efforts employing a combination of electron microscopy and synchrotron-based characterization techniques to quantify the effects of extended thermal ageing (up to 50,000hr at 360-700°C) on the microstructural properties of HT9, T91 and T92 ferritic- martensitic alloys. Changes in the microstructure were readily apparent from the qualitative and quantitative XRD analysis. Specific phases observed include BCC Fe host, FCC M23C6, HCP Laves (FeMo2), and FCC MX phase, with microstructures (weight fractions, lattice parameters and coherent grain sizes) all quantified as a function of ageing conditions. When coupled with electron microscopy, synchrotron-based XRD provides complimentary, and high throughput, insight across the multiple length scales needed to fill critical knowledge gaps to predict long-term behavior and performance in these important alloys. We highlight opportunities in leveraging synchrotron-based techniques to address applied materials science challenges to aid in developing physical understanding of thermally-induced microstructures in materials for future energy applications.

3:00 PM  
Intercritical Annealing of DP Steels Investigated by In Situ High Energy X-ray Diffraction Experiments: Clelia Couchet1; Kuan Hong Cheong1; Sébastien Allain1; Julien Teixeira1; Guillaume Geandier1; Frédéric Bonnet2; 1Institut Jean Lamour-Ijl (Cnrs Umr 7198); 2ArcelorMittal Maizières Research
    Austenite formation kinetics during intercritical annealing of various steels dedicated to the manufacturing of DP600/780 steels have been investigated in situ thanks to High Energy X-Ray Diffraction experiments. These experiments have been carried out on P07 beamline in PETRA III at DESY (Hamburg) with a monochromatic beam (100 keV). High flux from synchrotron source and fast high-throughput 2D detector (Perkin-Elmer) collects Debye-Scherrer (DS) diffraction patterns at significant rate (10hz). The effect of carbon content, niobium micro-alloying and cold-rolling ratio were studied along intercritical annealing between 780°C and 800°C using three heating rates (3°C/s, 30°C/s and 100°C/s). This work aims to provide better understanding for austenite morphogenesis during intercritical annealing and its interactions with recovery and recrystallization, which influence in turn the final mechanical properties of steels.

3:20 PM  
Improved Toughness of Warm-rolled Medium-Mn Steels Through Nano-sandwich Microstructure: Mun Sik Jeong1; Jeongho Han1; 1Hanyang University
    Here, we attempted to improve the toughness of medium-Mn steels through implementation of nano-sandwich microstructure via warm rolling. The hot-rolled and annealed (HRA) specimen exhibits the martensite and austenite with multi-variant laminate morphology. The warm-rolled (WR) specimen shows similar microstructure and phase fraction with HRA, however, it reveals the single directional laminate structure, which is aligned to rolling direction. The resulting microstructure is called nano-sandwich structure. The HRA shows the poor toughness, because the crack propagated rapidly along the PAGBs weakened by Mn segregation. However, WR showed improved toughness relative to HRA, because the cracking is suppressed by breaking of PAGBs during warm deformation. Besides, the crack could propagate in a direction perpendicular to the crack propagation, reducing the propagation energy and increasing the toughness; this phenomenon is called delamination. Therefore, it is expected that warm rolling is suggested as novel route for damage tolerant microstructural design of medium-Mn steel.

3:40 PM  
Precipitate and Texture Evolution in a Thick-gauge Niobium-microalloyed Line Pipe Steel: Monowar Hossain1; Xingshuo Wen2; Matthew Enloe3; Aaron Litschewski3; Murali Manohar2; Bertram Ehrhardt4; Gregory Thompson1; Nilesh Kumar1; 1University of Alabama, Tuscaloosa; 2ArcelorMittal – Global Research and Development; 3CBMM North America, Inc.; 4AM/NS Calvert
    Advances in processing and improved understanding of microstructural factors controlling mechanical properties have led to development of line pipe steels with high strength and toughness. However, the performance of line pipe steels is being further confronted by demand for thick-gauge steels to transport oil and gas at increasingly higher pressures. One of the challenges is reducing the microstructural heterogeneity through the thickness of heavy-gauge line pipe steels during processing. The focus of this work is on studying the precipitation and texture evolution through thickness in a Nb-microalloyed line pipe steel plate. Scanning electron microscope, transmission electron microscope, and electron backscattered diffraction were used to characterize chemistry and morphology of precipitates and texture. The initial results indicate that the precipitation and texture of the steel are different along the thickness and suggest a need for controlling composition, processing, or both to have uniform microstructure through the thickness of the steel plate.

4:00 PM Break

4:20 PM  
Post-partitioning Treatment to Improve Strength-ductility Combination in a Quench and Partitioning Steel: Berk Soykan1; Jiyun Kang1; Narayan Pottore2; Hong Zhu2; C. Tasan1; 1Massachusetts Institute of Technology; 2ArcelorMittal - Global Research and Development
    The essential role of steel as one of the world’s predominant structural materials can be proven by its broad spectrum of applications in machines, infrastructure, automotive, and defense. Developing lean steels with higher strength and ductility combinations is still an ongoing mission most recently addressed by the quench and partitioning (QP) process. However, one of the inevitable downsides of the QP process is the formation of fresh martensite after final quenching, which limits the ductility of such type of steel. In this work, we demonstrate that a post-partitioning treatment addresses this problem and further improves the damage resistance of QP steels. The underlying microstructural mechanisms contributing to such improvement are examined through a coupling of in-situ SEM/EBSD characterization and in-situ high-energy X-ray diffraction tensile testing. The resulting change in damage nucleation, growth, and coalescence processes are also discussed.

4:40 PM  
Characterization of Ductility and Microstructure Evolution in HSLA Microalloyed Steel during Continuous Casting: Alyssa Stubbers1; John Balk1; 1University of Kentucky
    Characterizing precipitation and phase transformation in Nb, Ti, V containing HSLA steels during simulated continuous casting processes presents challenges due to limited size of precipitates (<30 nm) and difficulty observing phase transformations during heating. Phase transformation and grain size characterization is challenging due to tendency of austenite to quench into martensite and few methods to observe phase transformation in-situ. Manual microscopy methods to identify precipitation are time consuming and have difficulty locating significant numbers of precipitates that can be meaningfully analyzed. Through use of in-situ dilatometry, ex-situ EBSD, and SAXS, the evolution of microstructures and their impact on hot ductility is evaluated to pinpoint mechanisms governing high-temperature, low-ductility behavior in microalloyed HSLA steels.